The present applicant has suggested various seat structures for improving the vibration-absorbing characteristic, the shock-absorbing characteristic, and the like, in which a cushion member is elastically supported by a frame supported by a torsion bar disposed in the front or back of a seat cushion part, or a cushion member is elastically supported by stretching the cushion member between side frames or front and back frames and supporting a part of the cushion member with a coil spring, thereby having the cushion member disposed as a tensile structure (see, for example, Patent Documents 1 and 2).